MicroRNAs (or miRNAs) are non-coding RNAs that are believed to act by incomplete base pairing with the 3'-untranslated region of target mRNAs leading to post-transcriptional gene silencing. We have identified novel miRNAs specific to the pancreatic islet. The miRNAs are conserved in mouse and human, suggesting a role in endocrine pancreas specification, and possibly glucose-induced secretion. We propose a series of molecular genetic, biochemical and bioinformatics studies to elucidate the molecular function of islet miRNA. In aim1, we will overexpress two novel islet-specific miRNAs in pancreatic beta cell lines and islets and study insulin secretion in response to a variety of insulin secretagogues. We will also inhibit miRNA function by transfecting 2'-O-methyl RNA oligonucleotides that are complimentary to the islet specific miRNAs. In aim 2, we will complete the generation of a mutant mouse in which the most abundant islet-specific miRNA has been replaced by a gene encoding a red fluorescent protein (RFP) by targeted "knock-in" and homologous recombination in ES cells. In aim3, we propose to use bioinformatic tools that will help in the identification of miRNA targets. Predicted targets will be validated in cell lines (aim1) and pancreatic islets (aim2).